Plate-like and irregularly shaped filler components, such as mica, aluminum flakes, inorganic minerals and coarsely ground rubber, can dissipate sound and vibration when oriented in either ordered or non-ordered multilayered arrays in a polymeric film. Many fillers are undesirable for use in waterborne sound deadening applications, however, because they can be difficult to incorporate into a sprayable product, they can exhibit water sensitivity, poor rheology and gassing, and they can be expensive.
Typically, precut asphalt- or rubber-based patches are used for lining floor pans, deck lids and doors of automobiles to dampen or reduce road and engine noise and vibration, preventing them from permeating into the passenger compartment of the motor vehicle. Sprayable coatings that are capable of being applied by robotics are desirable to provide labor and cost savings, reduced part inventories and flexibility in design specifications for damping properties. Waterborne or high solids coatings are desirable in trim shop applications where only air dry cure is feasible. It is desired that these coatings dry quickly, in about 2 to 3 hours after application, so that the coating does not transfer to other parts of the automobile during assembly operations.
Generally, any coating that contains a volatile component such as water must undergo a decrease in volume as the volatile component evaporates from the surface of the coating. As the volatile component leaves the coating, contraction forces act to pull the coating inward in all directions. Without intending to be bound by any theory, it is believed that if the coating has sufficient cohesive strength, the coating will contract in only one dimension; that is, the coating thickness will decrease while the coating resists contraction in any direction parallel to the substrate surface. By contrast, if a coating lacks cohesive strength sufficient to resist contraction parallel to the substrate surface, contraction forces will cause the coating to break up into small flat segments that are separated by continuous linear voids. This surface defect is commonly referred to as “mudcracking”.